#include<bits/stdc++.h>
using namespace std;
int main()
{
    double a,i;
    cin>>a;
    if(a<=15)
    {
        printf("%.2lf\n",a/1.5);
    }
    if(a>15)
    {
        printf("%.2lf\n",(a-15)/2.5+10);
    }
    return 0;
}
